Nowadays, handsfree devices providing a handsfree function by establishing a connection with a mobile phone handset are used widely. Some of the handsfree devices receive a ring-tone signal from a mobile phone handset, when the handsfree device is connected with the handset and the handset receives a phone call. Then the handsfree devices produce a ring-tone sound according to the received ring-tone signal.
For example, in the case that a handsfree device establishes the connection with a mobile phone handset by means of the Bluetooth (registered trademark), which is used widely in recent years, the handset transmits an in-band ring-tone signal to the handsfree device, when the handset receives a phone call. In this case, the handsfree device sometimes produces a ring-tone sound as it is represented by the in-band ring-tone signal. The word “in-band” refers to a manner of sending/receiving a signal wherein the signal is sent/received by means of a SCO link, which is defined by the Bluetooth.
However, there is no conventional mobile phone handset which changes, according to a signal from the handsfree device, the ring-tone signal to be sent. In an opinion of the inventor of the present invention, this may cause some inconveniences.
For example, the Bluetooth restricts a frequency range in which the in-band ring-tone signal is allowed to be transmitted.
In addition, the Bluetooth allows a master device to establish connections with up to seven devices. Therefore, the mobile phone handset and the handsfree device can establish connections with each other through a plurality of wireless channels (namely, SCO links) at a time.
The above restriction varies depending on a state of the connection (namely, number of the channels). For example, when the number of the channels with which the connections are established decreases, the frequency range in which the in-band ring-tone signal is allowed to be transmitted from the handset to the handsfree device is narrowed.
If the handset transmits the in-band ring-tone signal irrespective of the variation of the restriction, the ring-tone signal within a certain frequency range is distorted through the transmission. As a result, the handsfree device possibly produces a distorted sound (ring-tone sound).